Using a tv as an audio device

I have a small flat screen tv hooked up to my computer and I sometimes use it as the speakers for the computer when I dont want to use headphones.

Im having a problem with the volume level though. ill start playing music or a game or whatever and after a minute or so the sound will ramp down and I will have to turn the volume up on either the tv or the computers system volume to keep it where it was. However that often causes the sound to ramp way back up causing me to turn it back down only for it to get really quiet again.

Does anyone know whats causing this?

And no its not me turning the volume up or down too far. I will make small adjustments to the sound when it changes and it will go way up or way down after i stop adjusting the volume.

 

Go into Control Panel> Sound> Communications> Do Nothing. Might or might not fix it.

Already had that set... the TV is a vizio and is connected to the computer through an hdmi cable if that makes any difference.